(1) Field of the Invention
This invention relates to thermoplastic elastomeric compositions which can be fabricated into transparent films, webs, tubes, and other articles. More particularly, this invention relates to a composition of matter composed of a substantially uniform mixture of a thermoplastic elastomeric hydrocarbon block copolymer, mineral oil, and an essentially linear polysiloxane, as well as to the transparent articles, such as articles for medical applications, produced therefrom.
(2) Discussion of Prior Art and Problem To Be Solved
Highly advantageous elastomeric compositions and medical devices, such as medical tubing, are described in U.S. Pat. Nos. 4,386,179 and 4,481,323, both issued to Robert E. Sterling and assigned to Medical Research Associates, Ltd. #2, the assignee of this application. Unlike conventional elastomeric compositions, which are thermosetting in nature, these previously patented compositions are thermoplastic. Some of the principle advantages of these compositions, which have achieved wide commercial success under the "C-Flex" trademark, are their easy processibility, suitability for long term contact with human tissue, flexibility, elasticity, softness, smoothness, tensile strength, and absence of leachable substances. The C-Flex.RTM. compositions are composed of a substantially uniform mixture of a thermoplastic elastomeric hydrocarbon block copolymer, such as styrene-butadiene-styrene, or styrene-ethylenebutylene-styrene, mineral oil and an essentially linear polysiloxane, such as silicone oil, especially dimethylpolysiloxane. More generally, the polysiloxane is described by the following repeating structure: ##STR1## where R.sub.1, R.sub.2 =H, CH.sub.3 or ##STR2## and n is a positive number between 10 and 20,000.
While the compositions of the above-mentioned Sterling patents and medical tubing products using the patented C-Flex.RTM. compositions have achieved favorable recognition and success in the medical industry in view of their highly favorable properties as described above, these prior compositions all resulted in a somewhat cloudy or milky translucent material. As a result, the C-Flex.RTM. compositions were not totally acceptable for certain medical applications where it was important to be able to see the contents within the containers, tubing, etc. made from the C-Flex.RTM. material. For example, blood tubing, blood bags, transfusion tubing and bags, catheters, etc. are typical of the medical applications for which medical personnel may need to easily and quickly observe the contents within the bag, tubing, etc.
Accordingly, it would be highly desirable to provide compositions retaining all of the favorable characteristics and properties of the C-Flex.RTM. materials while improving their clarity and transparency.
Careful and detailed studies and research by the present inventors have led to the discovery that the cause of the cloudy or milky translucent property was apparently due, at least in part, to the insolubility of the polysiloxane in the mineral oil component. The present invention is based, at least in part, on the discovery that by utilizing polysiloxanes which are miscible in mineral oil in place of the polysiloxanes disclosed in the aforementioned Sterling patents, the compositions will provide clear transparent articles while retaining the other advantageous features and properties of the C-Flex.RTM. compositions.